機密保護 Conference Key Agreement Protocol Using Oblivious Transfer

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Conference key is one method for establishing secure communication among members of a group. Recently, much work has been done on the establishment of the conference key. However, when confirming the key, if each member signs the conference key which he/she has calculated, each member would need to verify that all members signed the conference key in order to verify that all members are holding the same conference key. In this case, using the conventional methods, each member needs to perform several decryptions, which contribute to a high computational burden to the group. The basic idea of our protocol is to establish a conference key based on oblivious transfer which can be used in both asymmetric and symmetric cryptography. Our protocol can reduce the number of decryptions for the key confirmation without sacrificing the level of security. In our proposed method, we break the conference key into several individual secret keys in accordance with the number of members within the group. This individual key will be used by each member to sign or encrypt(asymmetrically)the established conference key. To perform the key confirmation, each member multiplies all signed conference keys and decrypts(asymmetrically)the multiplied signed conference key using the multiplicative inverse of his locally calculated conference key. Thus, by using our proposed protocol, each member only needs to perform one decryption for the key confirmation. Furthermore, by using the individual secret key, each member can directly communicate with each other with the support of the leader, while the leader does not gain any knowledge of messages which are exchanged between the communicating members. This last feature can not be found in previous methods except for Li-Pieprzyk's. The difference between Li-Pieprzyk's and ours is that for the key generation, we need only a few modular exponentiations while the former needs much more.
一般社団法人情報処理学会の論文
2001-01-15

機密保護 Conference Key Agreement Protocol Using Oblivious Transfer

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